Don't mince words. In the extremely early days of YOUR startup, YOU didn't FEEL like you had much optionality. That is in no way universal. You very much do have optionality. You can quantify how much it costs to hire someone part time or full-time. You can quantify the risks of burning yourself out, or your manager can. Your firm had the optionality, you just chose to go in a very specific direction.
What I'm saying is that your firm survived in spite of, not because of this frankly amateurish decision.